Among the many changes that accompany adolescence are alterations in sleeping and waking patterns. These changes arise from numerous sources, including modified school-related demands, expanded social opportunities, alterations of parent-child relationships, involvement in athletics and part-time jobs, access to drugs and alcohol, and so forth. An altered physiological milieu may also have a marked impact upon an adolescent's sleep patterns. In recent years, the number of studies examining sleep patterns in adolescents using survey and laboratory methodology has increased. Nevertheless, a major gap in our understanding of adolescent sleep is in the careful assessment of youngsters as they pursue their daily lives. Tools are currently available to make significant strides in the assessment of adolescent sleep/wake patterns in field studies. Two specific issues will be pursued by the present application- both are logical extensions of previous work on this project. The first issue has to do with the ability of tans to accommodate to changes in sleep schedule that are imposed externally, for example, school schedules. One factor that may have a significant impact on a teen's ability to make such an adjustment is his or her circadian phase preference as measured using Morningness/Eveningness (M/E) scales. The second issue has to do with work schedules of older high school students. Many students work long hours outside of school, and some working students have markedly altered sleep schedules and impaired waking function. Significant gaps in our knowledge exist, however, regarding the types of work schedules that cause such impairments or types of students who are able to cope with working. Two studies are proposed to examine these issues. Study 1 will evaluate boys and girls across the 8th to 9th grade transition using a laboratory measure of physiological sleepiness (MSLT) along with field measures of sleep (actigraphy), mood, and introspective sleepiness (sleep diary). These measures will be made in children classified as "owls" or "larks" using an M/E scale. This study will examine the hypothesis that owls have more difficulty adjusting to the earlier school schedule demanded in 9th grade. Study 2 uses the same field measures to evaluate sleep-wake patterns in 11th and 12th grade boys and girls who work 25-35 hours per week or who are involved in organized athletics. Students will also be divided into groups in whom work or athletic training occurs before school on at least 3 days per week. Study 2 will test the hypothesis that working students have poorer sleep habits and are more impaired in the daytime than athletes; a secondary hypothesis is that all students with early morning commitments will sleep less and be more impaired than are those with no such morning activities.